If some of you played Alpha Centauri, when you finally have nearly beaten a computer, they told you "We surrender!! We will give you all our credit (3) and all our technology if you sign a blood truce!", and if you accepted, it was always : "All right, but you will have to become my Pact Brother", and then, they would be your VASSAL nation (Oh yhea! less micro-management). I then gave them back all the base I conquered (except those with really strategic importance), some of my technology, and used them as a front or distraction against other players. (if only they had a better AI...)
(And when came planetary council meeting, when I asked them "Vote this", they would answer a sweeeeet "as you wish" )
now, THAT would a great surrender option. The race swear they will follow your orders, and you protect them. They give tribute in return. Automatic-Allies, and they do as you ask. And you don't have to assume their stupid debts/crappy colonies/capitals. Yhea, you could tell them "gimme that, that, and that planet, these ships, etc..", and they would be forced to do so.
Less micro-management, and more realism. Even, if you loose in a war, "surrendering" would not always mean defeat if you surrender to the right guy. You could use their protection to slowly build up, until you try to "free yourself" of your oppressor! Loosing a war would not be the end or the game, and could allow great return!
What do ya think?